The present patent application is related to solid-state lighting devices.
Solid-state light sources, such as light emitting diodes (LEDs) and laser diodes, can offer significant advantages over other forms of lighting, such as incandescent or fluorescent lighting. For example, when LEDs or laser diodes are placed in arrays of red, green and blue elements, they can act as a source for white light or as a multi-colored display. In such configurations, solid-state light sources are generally more efficient and produce less heat than traditional incandescent or fluorescent lights. Although solid-state lighting offers certain advantages, conventional semiconductor structures and devices used for solid-state lighting are relatively expensive. One of the costs related to conventional solid-state lighting devices is related to the relatively low manufacturing throughput of the conventional solid-state lighting devices.
Referring to FIG. 1, a conventional LED structure 100 includes a substrate 105, which may, for example, be formed of sapphire, silicon carbide, or spinel. A buffer layer 110 is formed on the substrate 105. The buffer layer 110, also known as nucleation layer, serves primarily as a wetting layer, to promote smooth, uniform coverage of the sapphire substrate. The buffer layer 110 is typically formed of GaN, InGaN, AlN or AlGaN and has a thickness of about 100-500 Angstroms. The buffer layer 110 is typically deposited as a thin amorphous layer using Metal Organic Chemical Vapor Deposition (MOCVD).
A p-doped group III-V compound layer 120 is then formed on the buffer layer 110. The p-doped group III-V compound layer 120 is typically GaN. An InGaN quantum-well layer 130 is formed on the p-doped group III-V compound layer 120. An active group III-V compound layer 140 is then formed on the InGaN quantum-well layer 130. An n-doped group III-V compound layer 150 is formed on the group III-V layer 140. The p-doped group III-V compound layer 120 is n-type doped. A p-electrode 160 is formed on the n-doped group III-V compound layer 150. An n-electrode 170 is formed on the first group III-V compound layer 120.
One drawback of the above described convention LED structure 100 is the low manufacturing throughput associated with the small substrate dimensions. For example, sapphire or silicon carbide substrates are typically supplied in diameters of 2 to 4 inches. Another drawback of the above described convention LED structure 100 is that the suitable substrates such as sapphire or silicon carbide are typically not provided in single crystalline forms. The p-doped group III-V compound layer 120 can suffer from cracking due to lattice mismatch even with the assistance of the buffer layer 110. The p-doped group III-V compound layer 120 can suffer from cracking or delamination due to different thermal expansions between the p-doped group III-V compound layer and the substrate. As a result, light emitting performance of the LED structure 100 can be compromised.
Accordingly, there is therefore a need for a semiconductor structure and/or device that provides solid-state lighting using simpler processes and at reduced cost.